code: def __len__(self):
      return 10
  
file_path: audio/test/torchaudio_unittest/example/emformer_rnnt/test_mustc_lightning.py
imports: from contextlib import contextmanager
  from functools import partial
  from unittest.mock import patch
  import torch
  from parameterized import parameterized
  from torchaudio._internal.module_utils import is_module_available
  from torchaudio_unittest.common_utils import skipIfNoModule, TorchaudioTestCase
  from .utils import MockCustomDataset, MockDataloader, MockSentencePieceProcessor
label_desc: Use image node_id 3 for calling the MockMUSTC obj's underlying member method code with example usage: obj.__len__() and returns: int